LTC1530CS8 datasheet(12/24 Pages) LINER

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LTC1530

IRF7413 (both in SO-8) or Siliconix SUD50N03 or Motorola

MTD20N03HDL (both in DPAK) are small footprint sur-

face mount devices with RDS(ON) values below 0.03Ω at 5V

of VGS that work well in LTC1530 circuits. With higher

output voltages, the RDS(ON) of Q1 may need to be signifi-

cantly lower than that for Q2. These conditions can often

be met by paralleling two MOSFETs for Q1 and using a

single device for Q2. Using a higher PMAX value in the

RDS(ON) calculations generally decreases the MOSFET

cost and the circuit efficiency and increases the MOSFET

heat sink requirements.

In most LTC1530 applications, RDS(ON) is used as the

current sensing element. MOSFET RDS(ON) has a positive

temperature coefficient. Therefore, the LTC1530 IMAX sink

current is designed with a positive 3300ppm/

°C tempera-

ture coefficient. The positive tempco of IMAX provides first

order correction for current limit vs temperature. There-

fore, current limit does not have to be set to an increased

level at room temperature to guarantee a desired output

current at elevated temperatures.

Table 1 highlights a variety of power MOSFETs that are

suitable for use in LTC1530 applications.

PMAX should be calculated based primarily on required

efficiency or allowable thermal dissipation. A high effi-

ciency buck converter designed for the PentiumII with 5V

input and a 2.8V, 11.2A output might allow no more than

4% efficiency loss at full load for each MOSFET. Assuming

roughly 90% efficiency at this current level, this gives a

PMAX value of:

(2.8)(11.2A/0.9)(0.04) = 1.39W per FET

and a required RDS(ON) of:

DS ON Q

()

51 39

2 8

11 2

0 020

51 39

52 8

11 2

0 025

()









()

−

()







Ω

Note that while the required RDS(ON) values suggest large

MOSFETs, the power dissipation numbers are only 1.39W

per device or less — large TO-220 packages and heat

sinks are not necessarily required in high efficiency appli-

cations. Siliconix Si4410DY or International Rectifier

RDS(ON)

TYPICAL INPUT

AT 25

°C

RATED CURRENT

CAPACITANCE

θθθθθJC

TJMAX

MANUFACTURER

PART NO.

PACKAGE

(

Ω)

(A)

Ciss (pF)

(

°C/W)

(

°C)

Siliconix

SUD50N03-10

TO-252

0.019

15A at 25

°C

3200

1.8

175

10A at 100

°C

Siliconix

Si4410DY

SO-8

0.020

10A at 25

°C

2700

—

150

8A at 75

°C

ON Semiconductor

MTD20N03HDL

DPAK

0.035

20A at 25

°C

880

1.67

150

16A at 100

°C

Fairchild

FDS6680

SO-8

0.01

11.5A at 25

°C

2070

150

ON Semiconductor

MTB75N03HDL*

D2PAK

0.0075

75A at 25

°C

4025

1.0

150

59A at 100

°C

IRL3103S

D2PAK

0.014

56A at 25

°C

1600

1.8

175

40A at 100

°C

IRLZ44

TO-220

0.028

50A at 25

°C

3300

1.0

175

36A at 100

°C

Fuji

2SK1388

TO-220

0.037

35A at 25

°C

1750

2.08

150

Note: Please refer to the manufacturer’s data sheet for testing conditions and detailed information.

*Users must consider the power dissipation and thermal effects in the LTC1530 if driving external MOSFETs with high values of input capacitance.

Refer to the PVCC Supply Current vs GATE Capacitance in the Typical Performance Characteristics section.

Table 1. Recommended MOSFETs for LTC1530 Applications

APPLICATIO S I FOR ATIO

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